Using MMPs

The MMP enables you to mask the layout of your Messaging Server hosts
from your end users. Consequently, you assign users to a generic MMP or a
load balancer without having them point to the specific server where their
mail boxes reside. Message access clients point to the MMP for retrieving
incoming messages.

When such a client connects and authenticates, the MMP looks up the
user information in the directory to determine where the user’s messages
are held. The MMP then connects the client to that specific server. The following
figure shows how the MMP acts as a proxy for IMAP4 and POP3 connections to
Messaging servers. Figure 12–6 shows
how multiplexors function in a Messaging Server environment.

Figure 12–6 MMP Overview

Use a load balancer in front of the multiple MMPs. It is unlikely that
you would have a single MMP.

Using the MMP SMTP Proxy

The MMP contains an SMTP proxy that is designed to accept messages
but not transfer messages. Because of this design, never use the MMP SMTP
Proxy as the target of a DNS MX record or to otherwise receive mail incoming
from arbitrary sources on the Internet. Messaging Server does not support
the use of the MMP SMTP Proxy in a message transfer capacity.

Messaging Server does support the use of the MMP SMTP proxy for message
submission from end-user clients. However, the multiplexing functionality
of the MMP, which is necessary to distribute POP and IMAP connections to the
correct back-end store, is not necessary for SMTP submission. You can balance
SMTP submission by MX records for mail clients that follow the standard, or
by a simple load balancer for mail clients that do not follow the standard.

Only use the MMP SMTP Proxy in the following situations:

If the MTA is becoming impeded with SSL/TLS processing, the
MMP SMTP proxy can offload that processing for message submission while still
supporting standard SMTP STARTTLS.

If the MMP has SSL hardware acceleration for POP/IMAP, it
might make sense to also leverage that for SMTP submission.

If you need to use the "POP before SMTP" mechanism, then the
MMP SMTP Proxy is required.

The MMP SMTP proxy has a desired feature not present in the
back-end MTA.

If your deployment requires a proxy, then use the MMP SMTP
proxy, which is specifically designed to preserve the security features and
SMTP extensions present in the MTA and uses a custom SMTP extension (XPEHLO) to do so safely.

Note –

The MMP SMTP Proxy only works with Messaging Server's SMTP server
as a back-end.